[PATCH RFC v2 3/4] Break dependency between vcpu index in vcpus array and vcpu_id.

[Gleb Natapov <gleb@xxxxxxxxxx>]

Archs are free to use vcpu_id as they see fit. For x86 it is used as
vcpu's apic id.

Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
---
 include/linux/kvm_host.h |    1 +
 virt/kvm/kvm_main.c      |   45 ++++++++++++++++++++++++---------------------
 2 files changed, 25 insertions(+), 21 deletions(-)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index e9e0cd8..0934df3 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -132,6 +132,7 @@ struct kvm {
 					KVM_PRIVATE_MEM_SLOTS];
 	struct kvm_vcpu *bsp_vcpu;
 	struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
+	atomic_t online_vcpus;
 	struct list_head vm_list;
 	struct kvm_io_bus mmio_bus;
 	struct kvm_io_bus pio_bus;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5a55fe0..8f3fff8 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -693,11 +693,6 @@ out:
 }
 #endif
 
-static inline int valid_vcpu(int n)
-{
-	return likely(n >= 0 && n < KVM_MAX_VCPUS);
-}
-
 inline int kvm_is_mmio_pfn(pfn_t pfn)
 {
 	if (pfn_valid(pfn)) {
@@ -1713,15 +1708,12 @@ static int create_vcpu_fd(struct kvm_vcpu *vcpu)
 /*
  * Creates some virtual cpus.  Good luck creating more than one.
  */
-static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)
+static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
 {
 	int r;
 	struct kvm_vcpu *vcpu;
 
-	if (!valid_vcpu(n))
-		return -EINVAL;
-
-	vcpu = kvm_arch_vcpu_create(kvm, n);
+	vcpu = kvm_arch_vcpu_create(kvm, id);
 	if (IS_ERR(vcpu))
 		return PTR_ERR(vcpu);
 
@@ -1732,25 +1724,36 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, int n)
 		return r;
 
 	mutex_lock(&kvm->lock);
-	if (kvm->vcpus[n]) {
-		r = -EEXIST;
+	if (atomic_read(&kvm->online_vcpus) == KVM_MAX_VCPUS) {
+		r = -EINVAL;
 		goto vcpu_destroy;
 	}
-	kvm->vcpus[n] = vcpu;
-	if (n == 0)
-		kvm->bsp_vcpu = vcpu;
-	mutex_unlock(&kvm->lock);
+
+	for (r = 0; r < atomic_read(&kvm->online_vcpus); r++)
+		if (kvm->vcpus[r]->vcpu_id == id) {
+			r = -EEXIST;
+			goto vcpu_destroy;
+		}
+
+	BUG_ON(kvm->vcpus[atomic_read(&kvm->online_vcpus)]);
 
 	/* Now it's all set up, let userspace reach it */
 	kvm_get_kvm(kvm);
 	r = create_vcpu_fd(vcpu);
-	if (r < 0)
-		goto unlink;
+	if (r < 0) {
+		kvm_put_kvm(kvm);
+		goto vcpu_destroy;
+	}
+
+	kvm->vcpus[atomic_read(&kvm->online_vcpus)] = vcpu;
+	smp_wmb();
+	atomic_inc(&kvm->online_vcpus);
+
+	if (id == 0)
+		kvm->bsp_vcpu = vcpu;
+	mutex_unlock(&kvm->lock);
 	return r;
 
-unlink:
-	mutex_lock(&kvm->lock);
-	kvm->vcpus[n] = NULL;
 vcpu_destroy:
 	mutex_unlock(&kvm->lock);
 	kvm_arch_vcpu_destroy(vcpu);
-- 
1.6.2.1

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